The conventional article storage facilities described above perform storage operations in which the articles to be transported are picked up from an article carry-in-and-out portion, such as an article receiving platform, and are unloaded to a storage unit, retrieval operations in which the articles stored in the storage unit are picked up and are unloaded to the article carry-in-and-out portion, and relocating operations in which articles from certain storage units are picked up and are unloaded to other storage units, by performing article transporting operations with stacker cranes.
An article transporting operation of the stacker crane as the expression is used here means an operation of the stacker crane involving a traveling operation of the traveling carriage or the vertical movement operation of the vertically movable body, and includes, not only the actual transporting operation in which the article transfer device supporting the article to be transported is moved on the front side of the rack from the transport origin to the transport destination, but also includes, for example, an empty transporting operation in which the article transfer device supporting no article is moved to the transport origin by a travel operation and a vertical movement operation in order to pick up an article to be transported at the transport origin, as well as a return to origin operation in which the article transfer device supporting no article is moved to a home position in order to have the article transfer device stand by at the home position (starting point) arranged at an end in the direction of the travel path and at the lower end in the vertical direction to prepare for the subsequent storage operation after completing the storage operation.
And when an operation command for an storage operation or retrieval operation for an individual article unit is issued from a management computer with higher commanding status or from a command input means operated by an operator to input commands, the control means is configured to control the operation of the stacker crane to perform an article transporting operation, such as an actual transporting operation or the empty transporting operation, and an article transfer operation, such as a pick up operation for the article at the transport origin (pick up transfer operation) and an unloading operation of the article at the transport destination (unloading transfer operation), in order to have the storage operation or retrieval operation performed based on the operation command.
The travel operation and vertical movement operation in the article transporting operation are operations performed in accordance with a travel speed pattern and a vertical movement speed pattern which are determined based on the positional relationship between the operation starting position and the operation end position of the actual transporting operation and the empty transporting operation based on the operation command, allowing efficient movements, taking as little time as possible from the operation starting position to the operation end position by performing a suitable travel operation and a suitable vertical movement operation.
And, in the article storage facility describe above, a large number of articles that can be stored and retrieved per unit time, i.e., a high article throughput, which indicates the number of operation commands which can be processed, is desired to satisfy the need in the recent mass distribution age to shorten the time it takes to store and retrieve articles. Although various techniques are proposed to improve the article throughput in an article storage facility, it is suggested, for example, to provide a pair of stacker cranes, which can move along a travel path provided on the front side of the article storage rack and extending along the rack lateral width direction.
When providing a pair of stacker cranes to the one travel path, it is necessary to avoid the mutual interference between these stacker cranes. To this end, conventionally, when an operation command is issued, the control is such that a check is first performed to make sure that the other stacker crane, which would be an obstruction in the article transporting operation, is not located in the planned traveling range for the article transporting operation, before the stacker crane is caused to perform the article transporting operation (see, for example, Patent Document 1).
And when the other obstructing stacker crane is located in the planned traveling range for the article transporting operation, the operation of the other stacker crane is controlled to move it out of the planned traveling range if the other stacker crane is not performing an article transporting operation as a stacker crane in duty (that is, it is in a standby state). And if the other stacker crane is performing an article transporting operation as a stacker crane in its duty, the operation of the other stacker crane is controlled to move it out of the planned traveling range after waiting for the article transporting operation by the stacker crane to be completed.
In short, in the conventional article storage facility, when an operation command is issued, a check is made to see if other obstructing stacker cranes for the article transporting operation exist before causing the stacker crane to perform the article transporting operation, and when an obstructive stacker crane exists, an avoidance operation is performed in which the other stacker crane is caused to move to a location where it no longer presents an obstacle.
Incidentally, Patent Document 1 discloses only one common travel guide rail arranged in the travel path and a pair of stacker cranes arranged on this travel guide rail and in the direction of the travel path. And an intermediate section of the travel path is designated to be the shared section in which both stacker cranes can travel, and an exclusive section—where only one stacker crane can move—is designated on either side of the shared section to coincide with the relative positioning of the cranes in the direction of the travel path. And in an avoidance operation, the other stacker crane is moved out along the travel direction. According to FIG. 7 and the description in Paragraphs [0047] and [0048] of Patent Document 1, when an operation command is issued, if the other stacker crane is located in the shared section side area which is within the shared section in the planned traveling range, the travel movement is completed first in the exclusive section side area which belongs to the exclusive section in the planned traveling range. And the stacker crane is caused to wait in the part of the exclusive section side area near the shared section side area until the other obstructing stacker crane is moved out of the shared section side area, so that the article transporting operation can be completed as soon after the operation command is issued as possible based on the operation command.